1. Field of the Invention
The present invention relates to an optical system that controls the driving of an optical member on the basis of an operation on an operation unit.
2. Description of the Related Art
An optical system such as an imaging apparatus, a lens apparatus, and binoculars may have the known configuration in which an operation unit is operated to move an optical member such as a lens in accordance with the operated position (amount of operation) of the operation unit.
Japanese Patent Application Laid-Open No. 2006-258586 discloses an imaging apparatus in which a zoom ring is rotated to move a variable-power lens, which is mechanically connected thereto, through an interlock.
Japanese Patent Application Laid-Open No. 2004-233892 discloses an imaging apparatus in which a zoom ring is rotated to drive a zooming motor on the basis of the rotational position of a zoom ring detected by a rotational absolute position encoder and small-angle-displacement detected pulse encoder, which thus moves a variable-power lens. The variable-power lens is controlled so as to move to a target position on the basis of its position detected by the zoom encoder.
The configuration in which an operation unit such as a zoom ring is operated to move an optical member may require one-to-one correspondence between an operated position of the operation unit and the position of the optical member for higher operability for the operator.
In the configuration disclosed in Japanese Patent Application Laid-Open No. 2006-258586, a zoom ring and a variable-power lens are mechanically connected. Thus, whether the imaging apparatus is powered on or off, the operation on the zoom ring moves the variable-power lens, thus typically keeping the one-to-one correspondence between an operated position of the operation unit and the position of the optical member. However, the mechanical connection between the operation unit and the optical member may increase the complexity and the size of the device.
In the configuration disclosed in Japanese Patent Application Laid-Open No. 2004-233892, on the other hand, if the zoom ring is moved when the imaging apparatus is powered off, the one-to-one correspondence between the operated position of the operation unit and the position of the optical member is not satisfied.
If the zoom ring is not moved when the imaging apparatus is powered off, the operator may sometimes intend to photograph with the same zoom ratio as that before the power supply terminates (i.e., before the apparatus is powered off).
However, even if the zoom ring is not moved when the imaging apparatus is powered off, the lens may be moved to a position displaced from the position of the variable-power lens before it is powered off as a result of the control over the position of the variable-power lens based on the position of the zoom ring. This is because the zoom ring is recognized as being at a different rotational position from the position before the it is powered off even though the zoom ring stays at the same position due to a sensing error by an encoder that detects rotation of the zoom ring and/or a difference in resolution from the encoder that detects the lens position. As a result, though the operation unit is not moved, the zoom ratio differs between before it is powered off and after it is powered on again, which may reduce accuracy in the operability of the lens. These problems may occur similarly not only in the zoom ring but also in other operation units such as a focus ring.